In the past, ready-to-feed infant formulas have been prepared by the appropriate blending of ingredients, including varying proportions of selected animal fats to yield a composition having a protein, mineral, carbohydrate, and fatty acid composition approximating that of human milk fat. However, the fatty acids of such artificial formulations have not been as well absorbed by the infant, or by experimental animals, e.g., the laboratory rat, as are the natural fatty acids in milk.
Canadian patent No. 927,187 discloses a dietary product intended to adapt cow's milk to the requirements of human infants, and to make the cow's milk similar to human milk. The lipid component of this dietary product is preferably a mixture of vegetable oils with soy lecithin and eventually with milk fats.
Canadian Patent No. 927,188 discloses an edible fat composition intended to resemble that of human milk fat. This composition includes various proportions of oleic oil; oleo oil; a seed oil comprising at least one or more of soybean oil, corn oil, peanut oil, sunflower seed oil, and cottonseed oil; coconut oil and/or babassu oil; and soy lecithin.
The dietary products and fatty acid compositions disclosed in these patents rely upon edible oils, soy lecithin, and/or milk fats to form the lipid component. However, these oils do not contain the C.sub.20 and C.sub.22 omega-6 and omega-3 fatty acids which are present in human milk. Accordingly, these preparations do not provide a balance of fatty acids that are similar in composition to that of human milk.
It is known that the composition of dietary fat is a major determinant of tissue composition during the formative stage in the growth and development of an organ. An analysis of human milk at day 16 of lactation was used to estimate infants' daily intake of C.sub.20 and C.sub.22 omega-3 and omega-6 fatty acids. The study indicated that significant amounts of these fatty acids are normally received by the infant fed human milk.
Past studies have not resolved the nutritional biochemical question of how much and which essential fatty acids should be provided in a dietary formula to premature infants to ensure normal synthesis of nerve tissues. Such tissues would normally contain high levels of long-chain metabolites of essential fatty acids as basic structural material. In particular, it is important that the quantities of the C.sub.20 and C.sub.22, omega-3 and omega-6 fatty acids be limited to appropriate ranges in a dietary formula. Insufficient supply of these fatty acids would interfere with brain development. Over-feeding of these fatty acid could distort normal prostaglandin metabolism and thus have adverse effects on the infant's physiology. For example, providing too much of these fatty acids could result in over-production of prostaglandins in the gut, which could lead to a hyperactive gut and diarrhea.
Studies on the composition of human milk have identified further substances not found in many cow's milk-based formulas. Recently, it has been shown that human milk contains physiologically active concentrations of prostaglandins, specifically prostaglandin E.sub.2, prostaglandin F.sub.2.alpha., and the metabolites of prostaglandin I.sub.2, namely 6-keto-prostaglandin F.sub.1.alpha.. These prostaglandins and their metabolites are present in human milk at all stages of lactation and change in concentration during lactation in a manner analogous to the development of the infant's capacity to absorb nutrients. For example, in approximately the first three weeks of infant life, the level of these prostaglandins and their metabolites increases in human milk, as does the infant's capacity to absorb nutrients.
It is known that prostaglandins affect functions related to nutrient absorption. Thus, in the human a variety of physiological functions are affected in the gut by prostaglandins, e.g., gastric acid and mucous secretion, smooth muscle contraction, local circulation, nutrient transport, and absorption.
However, providing the optimum ratio of the omega-3 and omega-6 C.sub.20 and C.sub.22 fatty acids in an infant formula is essential in order to provide early nutrition. For a growing infant, DHA is more important that EPA. For example, DHA is required for growth of the retina, and 70% of the lipid sheath of nerves is composed of DHA. DHA is also required for brain and nerve development. Therefore, it is important that an infant formula provide sufficient DHA to the infant. Naturally occurring sources, such as fish oil, are generally used as a source of EPA and DHA for infant formula. For example, in U.S. Pat. No. 4,670,285, Clandinin et al. disclose an edible fat formula for feeding infants wherein the omega- and omega-6 fatty acids are derived from fish oil. Unfortunately, the ratio of EPA to DHA in fish oil is the reverse of what is required by a growing infant, and an insufficient amount of DHA is present in the formula.
A number of other infant formulas have been commercialized in an attempt to duplicate the nutritional value of mother's milk. However, to date, none of these formulas has proven completely acceptable in terms of infant nutrition, particularly for premature infants.
Tomarelli et al., in U.S. Pat. No. 3,542,560, disclose an infant formula having a fat similar to the fat in human milk, including palmitic acid.
Cannalonga et al., in U.S. Pat. No. 3,558,323, disclose a vitamin-containing composition in beadlet form, the vitamins being generally fat-soluble vitamins, which can then be incorporated in milk. When these beadlets are dispered in milk, they impart no off-flavor to the milk, and the beadlets can be mixed with spray-dried skim milk powder without affecting the stability of the powder.
Roberts, in U.S. Pat. No. 4,112,123, discloses a nutritionally balanced food composition for patients having abnormal catabolic states. These compositions include protein obtained from the ultra-filtration of sweet or acid wheys and contain .beta.-lactoglobulin, .alpha.-lactalbumin, immunoglobulins, and serum albumin. This food made be prepared in dried powder form to be reconstituted with a liquid. The powder may include encapsulated and embedded minerals.
Durst, in U.S. Pat. No. 4,800,087, discloses pharmaceutical compositions comprising a pharmaceutical core comprising a pharmaceutically active dose of a compound and a microencapsulating polymer which coats the pharmaceutical core and is capable of masking the taste of the active compound. The polymer coating does not fracture or release active ingredients when tabletted and/or chewed. These capsules may be included in a liquid formulation, although infant formula is not disclosed.